Influence of glucose on the sex ratio of bovine IVM/IVF embryos cultured in vitro

Abstract

The effect of glucose in the medium used during in vitro culture on the sex ratio of bovine blastocysts derived from in-vitro-matured and in-vitro-fertilized oocytes was evaluated. Oocytes were matured and inseminated with mixed sperm from three bulls and were cultured in vitro in modified synthetic oviducal fluid medium with 10% fetal calf serum, with or without glucose supplementation. The overall rate of cleaved embryos that developed to expanded blastocyst in the medium without glucose (27.0%) was significantly greater (P < 0.05) than the percentage observed when embryos were cultured in medium with glucose (17.5%). Analysis of variance was performed to analyse the effect of glucose on the proportion of male embryos reaching the blastocyst stage (or arrested at the morula stage) during Days 7 to 10. Regardless of the presence or absence of glucose in the medium, significantly (P < 0.05) more male than female embryos were harvested as expanded blastocysts on Day 7 and on Day 8 of culture. On Days 9 plus 10 of culture, a sex ratio imbalance only occurred in the absence of glucose in the culture medium (P < 0.05). Glucose did not produce any significant effect on the sex ratio of the overall number of expanded blastocysts harvested by Day 10 of in vitro culture. However a significantly greater proportion of females (P < 0.01) were found among those embryos that developed only to the morulae stage after 10 days in vitro. These results show that glucose supplementation of culture media produces a preferential loss of female embryos during culture to the blastocyst stage.

Sexual dimorphism among bovine embryos in their ability to make the transition to expanded blastocyst and in the expression of the signaling molecule IFN-τ

“…In our experiments, the phenomenon clearly results from a failure of female embryos cultured on the complex TCM-199 medium to make the transition to EB rather than from the faster growth of males. As suspected by Carvalho et al (22) and Gutierrez-Adan et al (47), glucose may be the reagent in the medium that is deleterious to female embryo development. Our data (Table 2) confirmed that a simple, glucose-free medium allowed female embryos to form EB as easily as males, and that the addition of 5.5 mM glucose to this medium was selectively detrimental to female EB formation.…”

“…In particular, the pentose phosphate pathway seems more active in in vitro-produced bovine blastocysts (48,51). In vitro culture also appears to lead to delayed X chromosome inactivation in female mammalian embryos (44,52) and to an increase in the mRNA for glucose 6-phosphate dehydrogenase and for other X-linked genes (47). Inactivation of the paternal X chromosome occurs in trophectoderm of female murine embryos at about the time of blastocele formation, whereas random X inactivation in the embryo proper occurs later (53,54).…”

“…Gutierrez-Adan et al (47) hypothesized that sexually dimorphic gene expression, such as that observed for glucose 6-phosphate dehydrogenase, may provide a means of controlling sex ratio in wild animal populations, by favoring the growth rate of male embryos over female embryos. Although our data suggest that growth rates of male and female embryos in culture are not different, a selective block to development, operating preferentially against one sex, would achieve the same purpose.…”

Sex-ratio adjustment in response to local mate competition is achieved through an alteration of egg size in a haplodiploid spider mite

“…In humans, sex differences have also been reported in the placental protein human chorionic gonadotropin (hCG) [10]. Concentration of glucose and other nutrients during early cell division might also influence secondary sex ratio, as higher levels of glucose favour the development and the implantation of male blastocysts, providing a potential mechanism for sex-ratio variation in relation to maternal condition (in bovines [11] and in mice [12,13]). Over the past few years, there has been increasing evidence that females are also able to control the sex of their offspring at conception, thus overcoming the rigid process of chromosomal sex determination (e.g.…”

Experimental alteration of litter sex ratios in a mammal

“…It is probable that more than one process could influence sex ratios (Sheldon & West 2004), and another mechanism by which sex ratios might be adjusted was suggested recently (Cameron 2004). Briefly, male and female conceptuses are sexually dimorphic in their response to glucose (Gutiérrez-Adán et al 2001) and in their ability to survive in mediums with different glucose concentrations ( Larson et al 2001). Added glucose enhances the development of the male conceptus, but inhibits female conceptus growth and development.…”